The above-captioned patent references disclose laser-based through silicon in-circuit logic analysis as applied to integrated circuits (ICs) that contain up to billions of gates or transistors. Laser-based through silicon in-circuit logic analysis can be performed, even on such huge ICs, since direct access to the active regions is available through the backside. Various techniques have been developed to allow access through the backside to determine voltages, parametrics, logic states, and other information or electrical properties of the electronic devices. However, inasmuch as each probe takes a certain amount of time, when billions of gates or transistors are subjected to through-silicon analysis, the time-on-tester (ToT) can become quite large. The amount of time-on-tester grows superlinearly as the size of the IC increases, and/or as the number of gates or transistors grows, and/or as the number of probes used to read logic values increases.
However, when performing failure analysis, it is often the case that the cause or suspected cause of a failure can be isolated to a particular portion or particular areas of the IC, and only certain areas need to be probed. Probing only certain areas of an IC can lead to significant time-savings. However what is needed is a technique to probe only specific points on an IC, and perform analysis based on only the data read from the probe points or diagnostic reports.
Thus, in order to address the problem of inexorably increasing time-on-tester (e.g., as ICs become more and more complex), techniques are needed to probe specific areas of an IC. More specifically, what is needed is a technique for performing precision probe positioning to take readings, which readings are then subjected to any form or forms of analysis.
Probes and sensors of various types (e.g., laser probes, photon sensors, etc.) can be applied in order to read or create perturbations of one or more active regions. Such probes and sensors take advantage of certain properties of the silicon substrate; in particular, the property that certain electromagnetic radiation (e.g., infrared light) can pass through the substrate, such that a portion of the radiation is reflected back through the substrate. Some such techniques are briefly discussed below:
Light Induced Voltage Alteration:
Reading perturbations of one or more active regions is sometimes possible using light-induced voltage alteration (LIVA). Using this technique, external test equipment (e.g., ATE) applies certain electrical potential and applies other conditions to the external connections of the IC to bring and hold the internal electrical states into a known static state. Then, external illumination is provided through the substrate of the IC (e.g., through to various internal areas). A change in the power supply demands from the external test equipment (e.g., ATE) as a result of perturbation from the external illumination is used to indicate the logic state of the device. Unfortunately, techniques used to date provide only gross measurements, and detection of the changes in logic are far slower than the clock rates of modern ICs, thus rendering this technique suited for only some forms of static analysis.
Photon Emission Mapping:
This legacy technique uses external test equipment to apply electrical conditions to the external connections of the IC, thus to move the internal electrical state to a particular state. Photons reflected from the various active areas at infrared (IR) wavelengths are detected with an IR camera. Emission strength indicates logic states across the field of view. Unfortunately, techniques used to date provide only gross measurements, and detection of the changes in the infrared wavelengths are far slower than the clock rates of modern ICs, thus rendering this technique suited for only some forms of static analysis.
Dynamic Laser Probing:
Laser-based illumination is reflected from the active regions carrying electronic perturbations at or near the active regions. The perturbations are converted into electrical signals by detectors. Electronic states within the IC are varied over a time period, and the changes in the perturbations are detected as the states vary over the same time period.
In some cases, the outputs of these detectors have been used with analog measurement tools to rasterize a field of view and to locate changing values that are changing at specific frequencies. Such detected frequencies are marked spatially with symbols on an image of the part. In other cases, these techniques use signal digitizing tools such as oscilloscopes. One application has been to display several cycles of a signal to measure rise time, pulse width, jitter, and other timing related parameters.
Unfortunately, the limitations inherent in the aforementioned light-induced voltage alteration, photon emission mapping, and dynamic laser probing techniques render such legacy techniques unable to meet the demands of high-speed wafer-level and at-speed testing.
Thus the time-on-tester and other practical problems attendant to the aforementioned legacy techniques can be addressed by performing precision probe positioning to take only a selected set of candidate readings, which candidate readings are then subjected to any form or forms of analysis.